Up to this time St. Basil is not seen to have publicly taken an active part in the personal theological discussions of the age; but the ecclesiastical world was eagerly disputing while he was working in Pontus. Aetius, the uncompromising Arian, was openly favoured by Eudoxius of Germanicia, who had appropriated the see of Antioch in 357. This provoked the Semiarians to hold their council at Ancyra in 358, when the Sirmian |Blasphemy| of 357 was condemned. The Acacians were alarmed, and manoeuvred for the division of the general council which Constantius was desirous of summoning. Then came Ariminum, Nike, and Seleucia, in 359, and |the world groaned to find itself Arian.| Deputations from each of the great parties were sent to a council held under the personal presidency of Constantius at Constantinople, and to one of these the young deacon was attached. The date of the ordination to this grade is unknown. On the authority of Gregory of Nyssa and Philostorgius, it appears that Basil accompanied his namesake of Ancyra and Eustathius of Sebaste to the court, and supported Basil the bishop. Philostorgius would indeed represent the younger Basil as championing the Semiarian cause, though with some cowardice. It may be concluded, with Maran, that he probably stood forward stoutly for the truth, not only at the capital itself, but also in the neighbouring cities of Chalcedon and Heraclea. But his official position was a humble one, and his part in the discussions and amid the intrigues of the council was only too likely to be misrepresented by those with whom he did not agree, and even misunderstood by his own friends. In 360 Dianius signed the creed of Ariminum, brought to Cæsarea by George of Laodicea; and thereby Basil was so much distressed as henceforward to shun communion with his bishop. He left Cæsarea and betook himself to Nazianzus to seek consolation in the society of his friend. But his feelings towards Dianius were always affectionate, and he indignantly repudiated a calumnious assertion that he had gone so far as to anathematize him. Two years later Dianius fell sick unto death and sent for Basil, protesting that at heart he had always been true to the Catholic creed. Basil acceded to the appeal, and in 362 once again communicated with his bishop and old friend. In the interval between the visit to Constantinople and this death-bed reconciliation, that form of error arose which was long known by the name of Macedonianism, and which St. Basil was in later years to combat with such signal success in the treatise Of the Spirit. It combined disloyalty to the Spirit and to the Son. But countervailing events were the acceptance of the Homoousion by the Council of Paris, and the publication of Athanasius' letters to Serapion on the divinity of the two Persons assailed. To this period is referred the compilation by Basil of the Moralia.
The brief reign of Julian would affect Basil, in common with the whole Church, in two ways: in the relief he would feel at the comparative toleration shewn to Catholics, and the consequent return of orthodox bishops to their sees; in the distress with which he would witness his old friend's attempts to ridicule and undermine the Faith. Sorrow more personal and immediate must have been caused by the harsh treatment of Cæsarea and the cruel imposts laid on Cappadocia. What conduct on the part of the Cæsareans may have led Gregory of Nazianzus to speak of Julian as justly offended, we can only conjecture. It may have been the somewhat disorderly proceedings in connexion with the appointment of Eusebius to succeed Dianius. But there can be no doubt about the sufferings of Cæsarea nor of the martyrdom of Eupsychius and Damas for their part in the destruction of the Temple of Fortune.
The precise part taken by Basil in the election of Eusebius can only be conjectured. Eusebius, like Ambrose of Milan, a layman of rank and influence, was elevated per saltum to the episcopate. Efforts were made by Julian and by some Christian objectors to get the appointment annulled by means of Gregory, Bishop of Nazianzus, on the ground of its having been brought about by violence. Bishop Gregory refused to take any retrogressive steps, and thought the scandal of accepting the tumultuary appointment would be less than that of cancelling the consecration. Gregory the younger presumably supported his father, and he associates Basil with him as probable sufferers from the imperial vengeance. But he was at Nazianzus at the time of the election, and Basil is more likely to have been an active agent.
To this period may be referred Basil's receipt of the letter from Athanasius, mentioned in Letter CCIV., § 6. On the accession of Jovian, in June, 363, Athanasius wrote to him asserting the Nicene Faith, but he was greeted also by a Semiarian manifesto from Antioch, of which the first signatory was Meletius.
Valentinian and Valens, on their accession in the following year, thus found the Church still divided on its cardinal doctrines, and the lists were marked in which Basil was henceforward to be a more conspicuous combatant.